1. Field of the Invention
The present invention relates to a novel menthol derivative. More specifically, the invention relates to a polymerizable menthol derivative, which is an optically active compound capable of being used as a chiral agent, a liquid crystal composition containing the menthol derivative, a polymer obtained from the composition, and use of them.
2. Description of the Related Art
A cholesteric liquid crystal molecule has a helical structure in its liquid crystal state. Accordingly, when a cholesteric liquid crystal having a helical structure having been fixed by polymerization is irradiated with light, it reflects circularly polarized light having a wavelength range that corresponds to the direction in rotation direction and the length of the pitch of the helix of the liquid crystal molecule. For example, when the cholesteric liquid crystal is irradiated with visible light, it selectively reflects light with wavelengths of blue, green, yellow and red corresponding to the length of the pitch of the liquid crystal. The color tone is different from that of a pigment or a dye, which shows color by absorption of light, and has viewing angle dependency, in which the color tone varies depending on the viewing angle. The length of the pitch of the cholesteric liquid crystal can be controlled by the temperature and the species of the compound, and thus the cholesteric liquid crystal can selectively reflect not only visible light but also light in the near infrared range or an ultraviolet range.
Such a material has been provided that selectively reflects light having a wavelength varying within a wide range by utilizing the characteristics of the cholesteric liquid crystal. Examples of the applications thereof include a liquid crystal pigment, a paint, a spray ink, a printing ink, a cosmetic product, an anticounterfeit printed matter and an ornamental article. Such applications have been proposed as an optical film for a polarizing plate, a compensation plate, a color filter and the like having an optical device such as a liquid crystal display device and a holography device. The cholesteric liquid crystal pigment as a known material is used as a cholesteric liquid crystal polymer in a flake form and a cholesteric liquid crystal in a form of microcapsules. Examples of the applications of the cholesteric liquid crystal pigment include a paint for automobiles and a cosmetic product.
A cholesteric liquid crystal can be generally prepared by adding an optically active compound (chiral agent) to a nematic liquid crystal. For reflecting circularly polarized light having a wavelength of from the ultraviolet range to the visible range, the cholesteric liquid crystal necessarily has a helical structure having an extremely short pitch. For attaining the helical structure having an extremely short pitch, an optically active compound having a large helical twisting power is demanded. When an optically active compound having a small HTP, the addition amount thereof is necessarily increased, which provides difficulty in control of the other properties, such as the temperature, at which a cholesteric liquid crystal appears, and the selected reflection wavelength range. In many cases, furthermore, an optically active compound does not exhibit liquid crystallinity, and when its addition amount is increased, the composition loses liquid crystallinity to fail to provide the intended cholesteric liquid crystal phase.
An optically active compound having a large HTP with a complex structure may require a laborious production process and thus may be an expensive material, which is not suitable for a mass-produced material in industrial scale.
JP-T-10-509726 and JP-A-3-72445 disclose polymerizable menthol derivatives, but there is a demand for development of a novel polymerizable menthol derivative.